1. Field of the Invention
The present invention relates to a semiconductor laser apparatus capable of emitting a plurality of light beams having different wavelengths and a method of manufacturing the same.
2. Description of the Background Art
A semiconductor laser device (infrared semiconductor laser device) emitting infrared light having a wavelength of about 780 nm has generally been applied to a CD (compact disk)/CD-R (compact disk-recordable) drive as a light source. Further, a semiconductor laser device (red semiconductor laser device) emitting red light having a wavelength of about 650 nm has been applied to a DVD (digital versatile disk) drive as a light source.
On the other hand, a DVD capable of recording and playback with blue-violet light having a wavelength of about 405 nm has recently been developed. In order to record and play this DVD, a DVD drive employing a semiconductor laser device (blue-violet semiconductor laser device) emitting the blue-violet light having the wavelength of about 405 nm has also been developed at the same time. This DVD drive requires compatibility with respect to the conventional CD/CD-R and the conventional DVD.
In this case, compatibility with respect to the conventional CD, the conventional DVD and a new DVD is implemented by a method of providing the DVD drive with a plurality of optical pickups emitting infrared light, red light and blue-violet light respectively or a method of providing an infrared semiconductor laser device, a red semiconductor laser device and a blue-violet semiconductor laser device in a single optical pickup. According to this method, however, the number of components is so increased that it is difficult to downsize the DVD drive, simplify the structure thereof and reduce the cost therefor.
In order to prevent such increase of the number of components, a semiconductor laser device formed by integrating an infrared semiconductor laser device and a red semiconductor laser device into one chip is put into practice.
However, while the infrared semiconductor laser device and the red semiconductor laser device formed on GaAs substrates can be integrated into one chip, it is extremely difficult to integrate a blue-violet semiconductor laser device not formed on a GaAs substrate with the infrared and red semiconductor laser devices into one chip.
Therefore, a light-emitting device having a structure obtained by preparing a monolithic red/infrared semiconductor laser device by forming an infrared semiconductor laser device and a red semiconductor laser device on the same chip, forming a blue-violet semiconductor laser device on another chip and thereafter stacking this chip of the blue-violet semiconductor laser device and the chip of the monolithic red/infrared semiconductor laser device with each other is proposed (refer to JP 2001-230502A, for example).
In the aforementioned light-emitting device, however, the infrared and blue-violet semiconductor laser devices share a common electrode in structure, and hence it is difficult to individually apply arbitrary voltages to the infrared semiconductor laser device, the red semiconductor laser device and the blue-violet semiconductor laser device respectively by a driving circuit. Therefore, the structure of the driving circuit has low flexibility, leading to a complicated structure.
Particularly in the aforementioned light-emitting device, a p-side electrode of the infrared semiconductor laser device and an n-side electrode of the blue-violet semiconductor laser device are electrically connected with each other with a bonding layer sandwiched therebetween. Thus, the driving system for the infrared semiconductor laser device and the blue-violet semiconductor laser device is inevitably limited. For example, the infrared semiconductor laser device and the blue-violet semiconductor laser device cannot be driven by a common-cathode driving system connecting n-side electrodes of the three devices in common or an anode-common driving system connecting three p-side electrodes in common.